The present invention relates generally to methods concerning the installation of tenons at the turbine blades of rotor assemblies of turbine systems by the application of a solid state bonding procedure that joins the tenons to the turbine blades so that covers or shrouds can be secured to the turbine blades by means of the tenons; and, in particular, the present invention relates to methods for the restoration, repair or replacement of the tenons at the turbine blades following damage to the tenons or the partial or complete removal of the tenons from the turbine blades such as for the purpose of removing the covers or shrouds secured to the turbine blades and addressing damage that can have occurred to the turbine blades or other components of the rotor assemblies for example.
The rotating component, or rotor assembly, of a turbine system such as a steam turbine system for example typically includes a central shaft, a disk or wheel secured to the shaft and turbine blades, or turbine buckets as they are often called, particularly with reference to their application to steam turbine systems, attached to the disk. The disk or wheel can be attached to the shaft by being integrally forged with the shaft or shrink fitted and keyed to the shaft for example. The turbine blades or turbine buckets are in turn secured around the circumference of the disk so that the fluid, such as a gas, vapor and/or liquid for example that is directed through the turbine system engages the turbine blades causing the turbine blades and attached disk to rotate thereby rotatably driving the central shaft. The torque produced at the rotating central shaft can be used to drive varieties of equipment such as compressors and electric generators for example. Securing means of various kinds familiar to those skilled in the art can be used to secure the turbine blades to the disk.
The turbine blades extend substantially radially from the turbine shaft and disk, and the ends of the turbine blades that extend radially the furthest distance from the turbine shaft and disk can be provided with tenons that can project outwardly substantially radially from the ends of the turbine blades. The tenons can be machined into the ends of the turbine blades when the turbine blades are manufactured or TIG-welded to the ends of the turbine blades for example. A cover or shroud that can comprise a complete annulus or ring-like structure that encircles the ends of all the turbine blades at which the tenons are located, or can comprise a plurality of segmented arcuate sections that individually encompass less than all the turbine blades but collectively encircle all the turbine blades at their ends, is secured to the ends of the turbine blades by means of the tenons. The cover includes openings the sizes and locations of which correspond with the dimensions and locations of the tenons at the ends of the turbine blades, allowing the tenons to pass through and protrude from the openings when the cover is in place at the ends of the turbine blades. The protruding portions of the tenons are peened or otherwise flattened or upset to secure the cover to the ends of the turbine blades. The cover serves to dampen and stiffen the reaction of the turbine blades to the impinging fluid that is directed through the turbine system and can also provide a circular band at which a seal can be located.
Once the cover is securely in place, access to the turbine blades and tenons, such as may be required to address damage to a turbine blade or tenon or the cover itself, for example, can only be had by removing at least the section of the cover that has been damaged or is located in the vicinity of the damaged blade or tenon. Typically, in that eventuality, the cover is removed by grinding away the portions of the tenons that have been flattened at the cover leaving beneath the cover a remnant of each of the tenons in place at the end of each respective turbine blade. The cover can thereafter be lifted away from the ends of the turbine blades and the necessary restorations, repairs and/or replacements made.
It may be necessary, particularly in the event a tenon has been seriously damaged to remove the remnant of the tenon after the cover has been removed. In any event, according to prior art practices, in connection with the performance of the necessary restorations, repairs and/or replacements, the tenons typically are returned to their original configuration by depositing weld material at the ends of the turbine blades and machining the weld material to a configuration that will allow the tenons to pass through the openings in the cover when the cover is replaced either by reinstalling the original cover or by seating a new cover in place. In those instances in which the tenon remnant has been entirely removed, the weld material is deposited directly onto the end of the turbine blade and in those instances in which a remnant of the tenon remains at the end of the turbine blade, the weld material is deposited on the tenon remnant.
Following the machining of the tenons and the replacement of the cover at the ends of the turbine blades, the portions of the restored tenons that protrude through the openings in the cover are flattened or upset as by peening for example in order to secure the cover to the turbine blades. Typically it will be necessary to subject the tenons to a post-weld heat treatment and because of that necessity, the turbine will have to be taken off-site to a location where heat treating facilities are available in order to completely perform the task of restoring the tenons. An example of a procedure as has been described is disclosed in U.S. Pat. No. 7,034,262 entitled “Apparatus and Methods for Repairing Tenons on Buckets” which is incorporated herein by reference